The invention relates to a method and an apparatus for the introduction of a combustible mixture from a carburetor or the like, through, at least one intake valve, into the cylinders of an internal combustion engine, in dependence on the position of the piston of the cylinder in question.
In known methods and apparatus, the introduction of the combustible mixture occurs through the camshaft-controlled intake valve, which is opened at the start or prior to the start of the "suction stroke" and which is closed at or after the termination of the suction stroke.
It is a known fact that the amount of mixture admitted into the working volume of the cylinder (called cylinder hereinafter) through the intake valve, due to the motion of the piston, is considerably smaller than the maximum amount which the cylinder could accept. As a result, the full power potential of the cylinder and, thus, of the entire internal combustion engine, is not exploited.
One of several causes for this only partial filling of the cylinder is the shape and method of operation of the intake valve, which is opened and closed by means of the camshaft and whose limited opening times play a large role, especially at high RPM, because the total opening time of the intake valve is relatively short, of the order of magnitude of hundreds of a second. In addition, the usual mushroom shape of the valve tappet represents a flow impedance to the aspirated mixture resulting in deceleration and deviation of the flow. The resulting reduction in the flow velocity necessarily leads to a reduction of the amount of mixture which can be introduced into the cylinder during the opening time.
Almost all known intake valves of this kind have a valve seat angle of 90.degree.. While it is known that the flow crossection is increased by approximately 20% in a valve with a seat angle of 120.degree., over that with a seat angle of 90.degree., a valve seat angle of 120.degree. leads to a still greater deceleration of the in-flowing mixture, whereby the advantage of the enlarged flow-crossection is largely offset.
Thus, the mushroom-shaped valve-tappet of presently customary intake valves necessarily represents an obstacle to the flow and opposes a complete filling of the cylinder with combustible mixture.
In order to remove this disadvantage, use has been made of injection pumps which force fuel into the cylinder when the camshaft-controlled intake valve opens, while the combustion air is simultaneously admitted. In this way, the amount of mixture introducible during the opening time of the intake valve is increased. However, such injection pumps are expensive and are usually employed only in large and expensive motor vehicles.
A further possibility for increasing the amount of mixture to be introduced consists of increasing the stroke of the intake valve and/or to prolong its opening time. Thus, for example, the intake valves of internal combustion engines in customary passenger vehicles have a stroke of approximately 4 mm, whereas engines of higher performance have a valve stroke of 6 mm, which is raised to 8 mm in racing cars. In the latter case, there is a simultaneous prolongation of the valve opening time.
While the increase of the valve stroke permits achieving a larger flow crossection for the mixture entering the cylinder, increasing the valve stroke also leads to higher speeds of motion of the valve tappet and, hence, to increased manifestations of wear and higher demands on the valve timing control. Nor is any worthwhile improvement achieved by increasing the flow crossection without increasing the valve stroke, because this increases the mass of the valve tappet to be moved, quite aside from the fact that the limited surface area of the cylinder head generally opposes such an enlargement of the valve crossection. The prolongation of the valve opening times can cause an overlap of the openings of the intake and outlet [exhaust] valves. Among other things, this shifts the maximum torque toward higher RPM and the engine exhibits poor idling.
It has also been attempted to provide several intake valves for each cylinder. But this requires an appropriately shaped and hence considerably more expensive camshaft, so that this solution also is not generally adopted.
For this reason, it has often been attempted to increase the performance of an internal combustion engine by increasing its RPM. This is successful up to a certain limit, even though it increases wear in the engine and changes the overall characteristics of the engine, but when the RPM increases, the amount of mixture which can be introduced into the combustion chamber decreases with increasing engine RPM, partly because of the shorter valve opening times, so that, above a certain RPM, the performance of the engine again declines sharply.
Thus, it is an object of the present invention to create a possibility to increase, in the simplest manner, the quantity of mixture to be introduced into the combustion chamber of the cylinder of an internal combustion engine. This is achieved, according to the invention, in a method of the kind mentioned above, in that, separately from the combustible mixture, combustion air is introduced into the cylinder in direct dependence on the pressure in the cylinder. Thus, in the method according to the invention, at least a part of the combustion air is no longer introduced into a cylinder through a valve controlled by the camshaft, but is introduced into the cylinder under direct control of the pressure; i.e. for example at the beginning of the suction stroke and hence at the onset of reduced pressure in the cylinder, a part of the combustion air is introduced into the cylinder controlled by this onsetting reduced pressure and independently of the camshaft timing.
Due to the fact that the supplementary combustion air does not enter through the usual, camshaft-controlled valve [and therefore the limitations caused thereby are eliminated] there results a substantially greater [generally complete] filling of the cylinder with combustible mixture, and, in this manner, a very large torque is achieved at low RPM.
As already mentioned, the pressure-dependent supply of combustion air can start at the beginning of the suction stroke of the piston and can end at the termination thereof, so that the total time available in principle is utilized for the introduction of combustion air.
Again as already mentioned, the amount of combustible mixture admitted into the cylinder decreases with increasing RPM of the engine. Thus, it is suitable if the proportion of the total mixture represented by the combustion air introduced in dependence on the pressure is increased as a function of engine RPM or is initiated only above a certain RPM and, hence, the decrease of the admitted amount of mixture with increasing RPM is avoided.
For application of the method according to the teachings of the present invention, each cylinder is provided preferably with at least one valve, controllable in dependence on the pressure in the cylinder, which can have the form of a check valve. Thus, in an advantageous embodiment, the inlet valve can include a movable ball and, on the side facing the combustion chamber, a ball support with lateral flow paths; on the side facing away from the combustion chamber, it may include a valve seat for the sphere.
No difficulty is encountered in constructing such inlet valves so as to generate the lowest possible friction losses and to require no lubrication while at the same time achieving very high flow velocities, -- leading to high turbulence and thus contributing to the possibility of using a lean mixture and to the complete combustion of the mixture in the combustion chamber. In addition, for a suitable flow direction, cooling of the camshaft-controlled intake valve results, and a reduction of the cylinder temperature. Furthermore, such inlet valves can open and close very abruptly as controlled by the pressure without requiring an especially large valve stroke. Thus, a full supply of combustion air is obtained virtually at the beginning of the opening movement, which is not the case with camshaft-controlled intake valves.
Preferably, the inlet valve is in direct communication with the surrounding air [aspirating combustion air] while the intake valve serves for the supply of a correspondingly "richer" mixture, with the result that a mixture with the desired mixture ratio is produced within the cylinder.
In order to increase the mixture supply as a function of RPM, it is possible to provide several inlet valves per cylinder, which are activated sequentially, for example by actuation of the gas pedal. In this way, the amount of mixture introduced per suction stroke can be very large even at high engine RPM.
It is also possible to permit actuation of the supplementary inlet valve only when a particular gas pedal position -- related to the engine RPM -- is reached. For this purpose, the gas pedal can be operatively connected by a shaft with the inlet valve. The shaft is disposed transversely within the supply aperture of the inlet valve and rotatable about its longitudinal axis and contains a bore therein which is in a transverse position with respect to the supply aperture of the inlet valve when the latter is in the inactive position so that the shaft closes the supply apertures; whereas the shaft is rotated by suitable control of the gas pedal so that the bore gradually releases the supply aperture of the inlet valve until it finally merges therewith.